How to clear cache on a Mac without breaking anything

Every guide to a slow Mac says clear your caches. Most of them do not say which ones, and a fair number tell you to delete the entire Caches folder, which is a bit like fixing a squeaky door by removing it.

Caches are also most of what cleaner apps count as “system junk”, which is why the number they report looks so alarming and why clearing it changes so little. A cache is a copy of something the computer can recreate but would rather not. Thumbnails, decoded images, downloaded fonts, compiled shaders. Clearing one costs you the time it takes to rebuild. That is the whole trade.

When it is genuinely worth doing

• An app is behaving strangely — showing stale content, failing to load images, refusing to update.
• You are short on disk space and an app’s cache has grown to gigabytes. Streaming apps and browsers are the usual offenders.
• Something looks wrong in the interface — wrong icons, wrong thumbnails.

When it is not

• General slowness. Caches make your Mac faster, not slower. Clearing them makes things briefly worse. If your Mac is slow, look at what is running, not at what is cached.
• As routine maintenance. There is no schedule on which this needs doing.

Where they are

Three places, in the order you should care:

du -sh ~/Library/Caches/* | sort -h | tail -15

~/Library/Caches is yours, and holds nearly everything worth clearing.

~/Library/Containers/<app>/Data/Library/Caches is where sandboxed apps put theirs, which is why an app can look like it has no cache while occupying several gigabytes.

/Library/Caches is system-wide, usually small — about 9 MB here — and rarely worth the risk.

Doing it without regretting it

Quit the app first. Deleting a cache underneath a running app leaves it holding references to files that no longer exist. Usually harmless, occasionally a crash.

Clear one app’s folder, not the whole directory. In Finder, ~/Library/Caches is a list of folders named com.vendor.app. Delete the contents of the one you want:

rm -rf ~/Library/Caches/com.vendor.app/*

Do not do this, however tempting:

rm -rf ~/Library/Caches/*

It works. It also signs you out of things, clears every browser cache at once, and leaves the next hour feeling sluggish as everything rebuilds. The disk space you get back is the same as clearing the three biggest folders individually.

Browser caches belong in the browser

Safari, Chrome and Firefox each keep their own, and each has a menu item that clears them properly while keeping your logins. Use those rather than deleting files:

• Safari — Settings → Advanced → Show features for web developers, then Develop → Empty Caches. For everything, History → Clear History.
• Chrome — Settings → Privacy and security → Delete browsing data.
• Firefox — Settings → Privacy & Security → Cookies and Site Data → Clear Data.

Doing it through the app means it clears the cache and leaves your sessions alone. Deleting the folder by hand does not make that distinction.

The system caches you cannot reach

Some caches are held open by macOS and cannot be cleared while it is running. Two mechanisms deal with them, and both are safer than anything you can do by hand.

A restart clears a set of them on the way down.

Safe Mode clears more. Boot into it, log in, then restart normally. On Apple silicon, shut down, hold the power button until “Loading startup options” appears, pick your disk, then hold Shift and click “Continue in Safe Mode”. On Intel, hold Shift during startup. This is the correct answer to font problems, icon corruption and “the Mac feels wrong since the update”.

What about the font cache?

Old guides recommend atsutil databases -remove. It still works, and it is still the right fix for genuinely garbled text or fonts that will not load. It is not a general speed fix, and you will need to restart afterwards.

After clearing

Expect the next launch of whatever you cleared to be slower than usual — that is the cache being rebuilt, and it is not a sign that something went wrong. If an app misbehaves afterwards, quit it fully and relaunch; that resolves nearly all of it.

If you find yourself doing this often for space rather than for a fault, the underlying problem is a specific app with an unbounded cache. Find it in that du output and take it up with its settings, not with the folder.